Wearable EMI Shielding Composite Films with Integrated Optimization of Electrical Safety, Biosafety and Thermal Safety

Abstract Biomaterial‐based flexible electromagnetic interference (EMI) shielding composite films are desirable in many applications of wearable electronic devices. However, much research focuses on improving the EMI shielding performance of materials, while optimizing the comprehensive safety of wearable EMI shielding materials has been neglected. Herein, wearable cellulose nanofiber@boron nitride nanosheet/silver nanowire/bacterial cellulose (CNF@BNNS/AgNW/BC) EMI shielding composite films with sandwich structure are fabricated via a simple sequential vacuum filtration method. For the first time, the electrical safety, biosafety, and thermal safety of EMI shielding materials are optimized integratedly. Since both sides of the sandwich structure contain CNF and BC electrical insulation layers, the CNF@BNNS/AgNW/BC composite films exhibit excellent electrical safety. Furthermore, benefiting from the AgNW conductive networks in the middle layer, the CNF@BNNS/AgNW/BC exhibit excellent EMI shielding effectiveness of 49.95 dB and ultra‐fast response Joule heating performance. More importantly, the antibacterial property of AgNW ensures the biosafety of the composite films. Meanwhile, the AgNW and the CNF@BNNS layers synergistically enhance the thermal conductivity of the CNF@BNNS/AgNW/BC composite film, reaching a high value of 8.85 W m‒1 K‒1, which significantly enhances its thermal safety when used in miniaturized electronic device. This work offers new ideas for fabricating biomaterial‐based EMI shielding composite films with high comprehensive safety.

The Sheet Resistance, EMI shielding, Anti-biofouling, Thermal Conductivity, and

Joule Heating Performance Measurements
An RTS-8 four-point probe tester examined sheet resistance (Rs) at the temperature of Among them, when SET > 15 dB, SEM can be usually ignored.
The anti-biofouling measurements were carried out with two model bacteria (gramnegative E. coli and gram-positive S. aureus).For antimicrobial evaluation, various single colonies were selected in 5 mL Luria-Bertani (LB) liquid medium and incubated at 180 rpm and 37 o C for 8−10 h to reach the logarithmic growth phase.Suitable concentrations were obtained by diluting the bacterial solutions with phosphate buffer (PBS, pH 7.4).All materials were dried and disinfected with UV irradiation for 60 min before use.The bacterial inhibitory capacity of the material was evaluated using the plate method.All experimental specimens (67 μg mL -1 ) were co-cultured with bacteria (approximately 3×106 CFU mL -1 each).To prevent the effect of heat and light on the test results, the ice packs were changed every 10 min.After 40 min of light, the bacterial solution was diluted and inoculated onto suitable agar and incubated at 37 o C for 12−14 h.The results were expressed as the total number of colony-forming units (CFU).

Bacterial inhibition was quantitatively evaluated by measuring the optical density (OD)
and the diameter of the inhibition circle of the nearby bacterial solution at 600 n.
The aforementioned composite films (3 mg well −1 ) were added into each well of a 48-well plate.The previous strains during the logarithmic growth period were diluted 10-fold in sterile saline (3×108 CFU mL −1 ).0.30 mL of the above bacterial solution was added to each well and cultured at 37 • C for 48 h to form biofilms.The integrity of bacterial biofilms [1] was evaluated by using the LIVE/DEAD BacLight Bacterial

S4
Viability Kit (Invitrogen, USA) and detecting the OD260 value of bacterial supernatant, which originated from the released DNA and RNA from the lysed cell.A widely used crystal violet staining assay was used for biofilm quantification. [2]In brief, the biofilms were gently washed with PBS to remove suspended bacteria.Then 0.1 mL of 4% paraformaldehyde was added into each well and kept for 10 min.After removing paraformaldehyde, each sample was stained with 0.10 mL of crystal violet dye for 15 min, and then rinsed in PBS.Afterward, 0.30 mL of absolute ethanol was added to release bound crystal violet.The color of each well was recorded by the camera.The absorbance quantification of the biofilms in each well was measured using a microplate reader at 570 nm.The changes in bacterial biofilms were further identified through SEM.The mats containing bacteria were collected and fixed in glutaraldehyde.
Subsequently, the samples were dehydrated gradually with a suite of ethanol-water mixtures, dried under vacuum until constant weight and observed through FE-SEM.
Thermal diffusivity (α) was performed on a NETZSCH LFA 467 Nano Flash at 25 °C.
The temperature changes of the center point of the composite films were monitored with a thermal imaging camera (E6, FLIR).
Joule heating performance was characterized by charging at a certain voltage supplied by a DC power supply (UTP 1306S, UNI-T), and the changes in surface temperature were monitored simultaneously by using a thermal imaging camera (E6, FLIR).

Figure S2 .
Figure S2.The cross-sectional SEM micrographs of BC film.

Figure S5 .S7Figure S6 .
Figure S5.The EMI SE of BC film in X-band.

Figure S11 .
Figure S11.Antibacterial and antibiofilm tests of different samples in E.coil and S.aureus bacterial suspensions.(a) Images and (b) size statistics of inhibitory zone diameter.

Table S3 .
Comparison of the EMI shielding performance in this work and previously reported composite films.

Table S4 .
Comparison of the EMI shielding performance in this work and previously reported composite films.

Table S5 .
Comparison of thermal conductivity in this work and reported literature.

Table S6 .
Comparison of comprehensive performance in this work and reported literature.